Q: Identify the sequence that is not arranged correctly.

Li < Be < B < C – first ionization potential. The correct option is right because the first ionization potential generally increases across a period from left to right due to increasing nuclear charge, which is not accurately reflected in the sequence provided.

Q: Identify the statement that is not correct:

The second ionization energy of Mg is higher than the second ionization energy of Na. The second ionization energy of Na (removing from the [Ne] core, ~4562 kJ/mol) is far higher than that of Mg (~1450). So 'IE2(Mg) higher than IE2(Na)' (option 1) is the incorrect statement - not the stored option 3, which is true.

Q: As stated by the Periodic Law, the changes in elemental properties depend on their

atomic numbers. The Periodic Law indicates that the properties of elements are periodic functions of their atomic numbers, meaning that as the atomic number increases, the elemental properties change in a predictable manner.

Q: Choose the sequence that arranges the following species in increasing order of size:

Ca2+ < K+ < Ar < Cl− < S2−. The correct option arranges the species based on their ionic or atomic radii, with cations being smaller than their neutral atoms and anions being larger. Ca2+ is the smallest due to losing two electrons, followed by K+, then neutral Ar, and finally Cl− and S2−, which are larger due to gaining electrons.

Q: Which of the following orderings is NOT in exact agreement with the property stated alongside it?

NH₃ < PH₃ < AsH₃ < SbH₃: increasing basic strength. The basic strength of these hydrides decreases down the group due to the increasing size and decreasing electronegativity of the central atom, making NH₃ a stronger base than PH₃, AsH₃, and SbH₃, which contradicts the stated order.

Q: Identify the sequence that is incorrect.

Li < Be < B < C — first ionization energy. First ionization energy order is Li < B < Be < C because the filled 2s2 of Be makes its IE higher than B's. So 'Li < Be < B < C' (option 1) is the incorrectly arranged sequence.

Question 1

For the element having atomic number 120, which symbol and IUPAC systematic name are correctly paired?

Accepted Answer

Ubn and unbinilium. The symbol 'Ubn' corresponds to the element with atomic number 120, and 'unbinilium' is the IUPAC systematic name that follows the naming convention for elements in this range, making this pairing correct.

Question 2

Which sequence correctly represents the ionization energies of carbon, nitrogen, and oxygen atoms?

Accepted Answer

C < N > O. The correct sequence reflects the increasing ionization energy trend across the second period of the periodic table, where carbon has the lowest ionization energy, nitrogen has a higher ionization energy due to its half-filled p subshell, and oxygen has a slightly lower ionization energy than nitrogen due to electron-electron repulsion in its p orbitals.

Question 3

Identify the sequence that is not arranged correctly.

Accepted Answer

Li < Be < B < C – first ionization potential. The correct option is right because the first ionization potential generally increases across a period from left to right due to increasing nuclear charge, which is not accurately reflected in the sequence provided.

Question 4

Identify the statement that is not correct:

Accepted Answer

The second ionization energy of Mg is higher than the second ionization energy of Na. The second ionization energy of Na (removing from the [Ne] core, ~4562 kJ/mol) is far higher than that of Mg (~1450). So 'IE2(Mg) higher than IE2(Na)' (option 1) is the incorrect statement - not the stored option 3, which is true.

Question 5

As stated by the Periodic Law, the changes in elemental properties depend on their

Accepted Answer

atomic numbers. The Periodic Law indicates that the properties of elements are periodic functions of their atomic numbers, meaning that as the atomic number increases, the elemental properties change in a predictable manner.

Question 6

Choose the sequence that arranges the following species in increasing order of size:

Accepted Answer

Ca2+ < K+ < Ar < Cl− < S2−. The correct option arranges the species based on their ionic or atomic radii, with cations being smaller than their neutral atoms and anions being larger. Ca2+ is the smallest due to losing two electrons, followed by K+, then neutral Ar, and finally Cl− and S2−, which are larger due to gaining electrons.

Question 7

Which of the following orderings is NOT in exact agreement with the property stated alongside it?

Accepted Answer

NH₃ < PH₃ < AsH₃ < SbH₃: increasing basic strength. The basic strength of these hydrides decreases down the group due to the increasing size and decreasing electronegativity of the central atom, making NH₃ a stronger base than PH₃, AsH₃, and SbH₃, which contradicts the stated order.

Question 8

Identify the sequence that is incorrect.

Accepted Answer

Li < Be < B < C — first ionization energy. First ionization energy order is Li < B < Be < C because the filled 2s2 of Be makes its IE higher than B's. So 'Li < Be < B < C' (option 1) is the incorrectly arranged sequence.

Question 9

Which of the following gives the correct decreasing order of electron gain enthalpy (with negative sign) for fluorine, chlorine, bromine and iodine, whose atomic numbers are 9, 17, 35 and 53 respectively?

Accepted Answer

Cl > F > Br > I. Chlorine has the highest electron gain enthalpy due to its optimal size and effective nuclear charge, making it easier to gain an electron. Fluorine, while highly electronegative, experiences greater electron-electron repulsion in its small atomic radius, resulting in a slightly lower electron gain enthalpy than chlorine. Bromine and iodine have larger atomic sizes, leading to a decrease in their ability to attract additional electrons, thus placing them lower in the order.

Question 10

Among the following ions, which one has the greatest ionic radius?

Accepted Answer

O²⁻. O²⁻ has the greatest ionic radius because it has gained two electrons, resulting in increased electron-electron repulsion and a larger size compared to the other ions listed, which have either lost electrons or gained fewer.

Question 11

Which of the following sequences gives the correct increasing order from the least negative to the most negative electron gain enthalpy for C, Ca, Al, F and O?

Accepted Answer

Ca < Al < C < O < F. The correct order reflects the trend in electron gain enthalpy, where elements like Ca have a low tendency to gain electrons due to their larger atomic size and lower effective nuclear charge, while F has a high electron gain enthalpy due to its high electronegativity and small size, making it more favorable to gain an electron.

Question 12

In its period, which element shows both strongly electropositive and strongly electronegative behavior?

Accepted Answer

Hydrogen. Hydrogen exhibits both electropositive behavior, as it can lose its single electron to form cations, and electronegative behavior, as it can gain an electron to form anions, making it unique among the elements.

Question 13

Among the following ions, which one has the largest ionic radius?

Accepted Answer

O²⁻. O²⁻ has the largest ionic radius because it has gained two electrons, resulting in increased electron-electron repulsion and a larger size compared to the other ions listed, which either have fewer electrons or are positively charged.

Question 14

Select the sequence that shows the ions in order of increasing ionic radius (from smallest to largest): O²⁻, S²⁻, N³⁻, and P³⁻.

Accepted Answer

O²⁻ < N³⁻ < S²⁻ < P³⁻. The correct sequence is based on the increasing number of electron shells and the effective nuclear charge experienced by the ions. As we move from O²⁻ to P³⁻, the ionic radius increases due to the addition of electron shells and a decrease in effective nuclear charge, leading to a larger size.

Question 15

Identify the incorrect statement from the following:

Accepted Answer

All isoelectronic ions are found in the same period of the periodic table.. Isoelectronic ions are NOT all in the same period (e.g. N3-, O2-, F- are period 2 while Na+, Mg2+ are period 3), so statement 1 is the incorrect one. The stored choice (vdW radius > covalent radius) is actually true.

Question 16

The first ionization enthalpy (ΔH₁), second ionization enthalpy (ΔH₂), and electron gain enthalpy (ΔegH), all in kJ mol⁻¹, for five elements I, II, III, IV and V are listed below:

Element ΔH₁ ΔH₂ ΔegH
I 520 7300 -60
II 419 3051 -48
III 1681 3374 -328
IV 1008 1846 -295
V 2372 5251 +48

Fro

Accepted Answer

II and V. Element II has a relatively low first ionization enthalpy, indicating it can easily lose an electron, making it the most reactive metal. Element V has a positive electron gain enthalpy, suggesting it does not favorably gain electrons, which characterizes it as the least reactive non-metal.

Question 17

Examine the statements below:
(i) As we move from left to right across a period, atomic size generally decreases.
(ii) As we go from top to bottom in a group, atomic size generally increases.
(iii) Even though the periodic table is arranged according to atomic number, elements in the same

Accepted Answer

(i), (ii) and (iii). Atomic size decreases across a period (i), increases down a group (ii), and same-group elements show similar chemistry (iii) - all three are true, so the answer is (i), (ii) and (iii). The stored answer omits the true statement (ii).

Question 18

The first and second ionisation energies (in kJ mol⁻¹) of four elements labeled I, II, III and IV are listed below. Which one is an alkali metal?

IE₁	IE₂
I	2372	5251
II	520	7300
III	900	1760
IV	1680	380

Accepted Answer

II. Element II has a significantly lower first ionisation energy compared to the others, which is characteristic of alkali metals. Alkali metals have one electron in their outer shell, making it easier to remove, resulting in lower ionisation energies.

Question 19

If the first ionisation energy of sodium is 5.1 eV, what is the electron gain enthalpy of Na+?

Accepted Answer

−5.1 eV. Adding an electron to Na+ to reform Na is the exact reverse of the first ionization, so the electron gain enthalpy of Na+ = -5.1 eV, not -2.55 eV.

Question 20

Consider the elements Mg, Al, Si, P and Si, the correct increasing order of their first ionization enthalpy is:

Accepted Answer

Al < Mg < Si < S < P. Across period 3, IE rises but with two dips: Al < Mg because Al loses a 3p electron (higher energy, easier) vs Mg's filled 3s; and S < P because P has a stable half-filled 3p^3. So the order is Al < Mg < Si < S < P.

Question 21

The group having isoelectronic species is:

Accepted Answer

O²⁻, F⁻, Na⁺, Mg²⁺. The correct option includes species that all have the same number of electrons, specifically 10 electrons each, making them isoelectronic. O²⁻, F⁻, Na⁺, and Mg²⁺ all correspond to the electron configuration of neon, which confirms their isoelectronic nature.

Question 22

Which of the following gives the descending order of ionic radii for the species listed?

Accepted Answer

O2− > F− > Na+ > Mg2+ > Al3+. The correct option is based on the principle that anions are generally larger than cations due to the addition of electrons, which increases electron-electron repulsion. Among the listed species, O2− is the largest anion, followed by F−, while Na+, Mg2+, and Al3+ are cations with decreasing ionic radii as their positive charge increases.

Question 23

Which of the following sequences correctly represents the electron gain enthalpy values with negative sign for F, Cl, Br and I (atomic numbers 9, 17, 35 and 53, respectively)?

Accepted Answer

Cl > F > Br > I. Chlorine has the highest electron gain enthalpy due to its smaller atomic size and greater effective nuclear charge compared to fluorine, which is less favorable for gaining an electron. As we move down the group from Cl to I, the electron gain enthalpy decreases because the atomic size increases, making it less energetically favorable to add an electron.

Question 24

Which of the following sequences shows the elements Ca, Ba, S, Se and Ar arranged in the correct order of increasing first ionization enthalpy?

Accepted Answer

Ba < Ca < Se < S < Ar. The correct order of increasing first ionization enthalpy reflects the general trend in the periodic table, where ionization energy increases across a period and decreases down a group. Barium (Ba) has the lowest ionization energy due to its larger atomic size and lower effective nuclear charge, followed by calcium (Ca), while sulfur (S) and selenium (Se) have higher ionization energies due to their position in the p-block, with argon (Ar) having the highest ionization energy as a noble gas.

Question 25

What are the ionic radii (in Å) of N3−, O2− and F−, respectively?

Accepted Answer

1.71, 1.40 and 1.36. The correct option lists the ionic radii of N3−, O2−, and F− in decreasing order, reflecting the trend that larger anions have greater ionic radii due to increased electron-electron repulsion and the number of electrons relative to protons.

Question 26

Among the following atoms, which one has the greatest first ionization energy?

Accepted Answer

Sc. Scandium (Sc) has a higher first ionization energy than potassium (K), rubidium (Rb), and sodium (Na) because it is located further to the right in the periodic table, where atoms have a stronger effective nuclear charge and hold onto their electrons more tightly.

Question 27

Which pair of periodic properties generally shows a downward trend and an upward trend, respectively, as you move from top to bottom within a group?

Accepted Answer

Electronegativity and atomic size.. As you move down a group in the periodic table, atomic size increases due to the addition of electron shells, while electronegativity decreases because the increased distance between the nucleus and the valence electrons reduces the nucleus's ability to attract bonding electrons.

Question 28

Which element shows the largest gap between its first and second ionization enthalpies?

Accepted Answer

K. Potassium (K) has a significant gap between its first and second ionization enthalpies because removing the first electron results in a stable noble gas configuration, while the second ionization requires removing an electron from a more stable, inner shell, which requires much more energy.

Question 29

Which of the following gives the electron gain enthalpies (in kJ/mol) of fluorine, chlorine, bromine and iodine in that order?

Accepted Answer

−333, −349, −325 and −296. The correct option reflects the trend in electron gain enthalpy values, which generally become less negative down the group in the halogens due to increasing atomic size and decreasing effective nuclear charge, making it easier for larger atoms to accommodate an additional electron.

Question 30

The first ionisation potential of Na is 5.1 eV. The value of electron gain enthalpy of Na+ will be

Accepted Answer

-5.1 eV. The electron gain enthalpy of Na+ is equal in magnitude but opposite in sign to the first ionisation potential of Na, as it represents the energy change when an electron is added to a positively charged ion. Therefore, since the ionisation potential is 5.1 eV, the electron gain enthalpy for Na+ is -5.1 eV.

Question 31

The atomic radius of Ag is closest to:

Accepted Answer

Au. Silver (Ag) and gold (Au) are both in the same group of the periodic table, which means they have similar atomic structures and properties, including atomic radius. As you move down a group, the atomic radius generally increases, making Au the closest match to Ag.

Question 32

Which of the following represents the correct order of increasing first ionization enthalpy for Ca, Ba, S, Se and Ar ?

Accepted Answer

Ba < Ca < Se < S < Ar. The first ionization enthalpy generally increases across a period and decreases down a group. Barium (Ba) is in Group 2 and has the lowest ionization energy due to its larger atomic size, followed by calcium (Ca), while sulfur (S) and selenium (Se) are in Group 16 and have higher ionization energies, with argon (Ar) having the highest due to its stable noble gas configuration.

Question 33

The first ionisation potential of Na is 5.1 eV. The value of electron gain enthalpy of Na+ will be -

Accepted Answer

-5.1 eV. The electron gain enthalpy of Na+ is equal in magnitude but opposite in sign to the ionization potential of Na, as it reflects the energy change when an electron is added to Na+. Therefore, since the ionization potential is 5.1 eV, the electron gain enthalpy for Na+ is -5.1 eV.

Question 34

Which of the following atoms has the highest first ionization energy ?

Accepted Answer

Sc. Scandium (Sc) has a higher first ionization energy compared to rubidium (Rb), sodium (Na), and potassium (K) because it is located further to the right in the periodic table, where elements generally have a stronger attraction between the nucleus and their outer electrons, making it more difficult to remove an electron.

Question 35

The correct order of electron affinity is - [JEE-Main On line-2018]

Accepted Answer

Cl > F > O. Chlorine has the highest electron affinity among the three elements due to its effective nuclear charge and smaller atomic radius, which allows it to attract additional electrons more readily than fluorine and oxygen.

Question 36

For Na+, Mg2+, F− and O2−, the correct order of increasing ionic radii is:

Accepted Answer

Mg2+ < Na+ < F− < O2−. O2-, F-, Na+, Mg2+ are all isoelectronic (10 electrons). Radius decreases as nuclear charge rises, so increasing order is Mg2+(12p) < Na+(11p) < F-(9p) < O2-(8p).

Question 37

All species are isoelectronic (10e−). Isoelectronic series, when negative charge increases the radius of ion increases. Mg2+ < Na+ < F− < O2−

Accepted Answer

Mg2+ < Na+ < F− < O2−. The correct option reflects the increasing ionic radius as the negative charge increases in an isoelectronic series. As more electrons are added, the electron-electron repulsion increases, leading to a larger radius, which is accurately represented by the order Mg2+ (smallest) to O2− (largest).

Question 38

The correct option with respect to the Pauling electronegativity values of the element is: (1) Ga < Ge (2) Si < Al (3) Te > Se (4) P > S

Accepted Answer

Ga < Ge. Gallium has a lower electronegativity than germanium due to its position in the periodic table, where gallium is located in the same group as aluminum but has additional electron shielding that reduces its effective nuclear charge on valence electrons.

Question 39

When the first electron gain enthalpy (ΔegH) of oxygen is -141 kJ/mol, its second electron gain enthalpy is:

Accepted Answer

a positive value. Adding a second electron to the already negative O- ion requires energy to overcome electron-electron repulsion, so the second electron gain enthalpy of oxygen is positive (endothermic).

Question 40

The IUPAC symbol for the element with atomic number 119 would be -

Accepted Answer

(1) uue. IUPAC numeral roots: 1=un, 9=enn. Atomic number 119 = un-un-enn -> symbol Uue.

Question 41

The correct order of the atomic radii of C, S, Al and Cs is:

Accepted Answer

C < S < Al < Cs. C (~77 pm) < S (~104 pm) < Al (~143 pm) < Cs (~262 pm). Al is left of S in the same period so Al > S, and Cs is largest, giving C < S < Al < Cs.

Question 42

Among the statements (I – IV), the correct ones are:
(I) Be has smaller atomic radius compared to Mg.
(II) Be has higher ionization enthalpy then Al.
(III) Charge/radius ratio of Be is greater than that of Al.
(IV) Both Be and Al form mainly covalent compounds.

Accepted Answer

(2) (I), (II) and (IV). (I) Be radius < Mg radius: true. (II) IE of Be (~899) > Al (~577): true. (IV) Be and Al both form mainly covalent compounds: true. (III) is the doubtful one. The valid combination is (I),(II) and (IV).

Question 43

The five successive ionization enthalpies of an element are 800, 2427, 3658, 25024 and 32824 kJ mol⁻¹. The number of valence electron in the element is -

Accepted Answer

(1) 3. Successive IEs 800, 2427, 3658 then a huge jump to 25024 indicate three easily-removable electrons before reaching a stable core. Therefore the element has 3 valence electrons.

Question 44

The atomic radius of Ag is closest to:

Accepted Answer

Au. Due to the lanthanide contraction, gold (Au) has almost the same atomic radius (~144 pm) as silver (Ag), so Ag is closest to Au.

Question 45

The first ionization energy (in kJ/mol) of Na, Mg, Al and Si respectively, are:

Accepted Answer

496, 737, 577, 786. The correct option reflects the increasing trend in ionization energy across the period, where sodium has the lowest ionization energy due to its single valence electron, and silicon has a higher ionization energy due to its greater nuclear charge and electron configuration.

Question 46

The increasing order of the atomic radii of the following elements is: (a) C (b) O (c) F (d) Cl (e) Br

Accepted Answer

(c) < (b) < (a) < (d) < (e). The atomic radius generally increases down a group in the periodic table due to the addition of electron shells, while it decreases across a period from left to right due to increased nuclear charge. In this case, fluorine (F) has the smallest radius, followed by oxygen (O), carbon (C), chlorine (Cl), and bromine (Br), which aligns with the correct option.

Question 47

B has a smaller first ionization enthalpy than Be. Consider the following statements:
(i) it is easier to remove 2p electron than 2s electron
(ii) 2p electron of B is more shielded from the nucleus by the inner core of electrons than the 2s electrons of Be
(iii) 2s electron has more penetr

Accepted Answer

(2) (i), (ii) and (iii). (i) True: the 2p electron of B is easier to remove than the 2s electron of Be. (ii) True: the 2p electron is more shielded by the inner core. (iii) True: 2s penetrates more than 2p. (iv) False: B has a SMALLER atomic radius than Be. So the correct set is (i), (ii), (iii).

Question 48

The characteristics of elements X, Y and Z with atomic numbers, respectively, 33, 53 and 83 are:

Accepted Answer

X is a metalloid, Y is a non-metal and Z is a metal.. Element X (atomic number 33) is arsenic, a metalloid; element Y (atomic number 53) is iodine, a non-metal; and element Z (atomic number 83) is bismuth, a metal. This classification aligns with the periodic table's categorization of these elements based on their properties.

Question 49

The correct order of conductivity of ions in water is:

Accepted Answer

Cs+ > Rb+ > K+ > Na+. In water, larger bare cations are less hydrated and move faster, so conductivity order is Cs+ > Rb+ > K+ > Na+. The correct option is Cs+ > Rb+ > K+ > Na+.

Question 50

Outermost electronic configuration of a group 13 element, E, is 4s² 4p¹. The electronic configuration of an element of p-block periodic table placed diagonally to element E is:

Accepted Answer

[Kr] 4d¹⁰ 5s² 5p². The correct option represents an element in the same group as element E but in the next period, following the diagonal relationship in the periodic table. This means it has a similar outermost electronic configuration with an increase in principal quantum number, which is consistent with the properties of elements in the p-block.

JEE Main Chemistry: Classification of Elements and Periodicity questions with solutions

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